Photonic CrystalsDOI: 10.1002/anie.201412475

Mechanochromic Photonic-Crystal Fibers Based on Continuous Sheetsof Aligned Carbon Nanotubes**Xuemei Sun,* Jing Zhang, Xin Lu, Xin Fang, and Huisheng Peng*

Abstract: A new family of mechanochromic photonic-crystalfibers exhibits tunable structural colors under stretching. Thisnovel mechanochromic fiber is prepared by depositing poly-mer microspheres onto a continuous aligned-carbon-nanotubesheet that has been wound on an elastic poly(dimethylsiloxane)fiber, followed by further embedding in poly(dimethylsil-oxane). The color of the fiber can be tuned by varying the sizeand the center-to-center distance of the polymer spheres. Itfurther experiences reversible and rapid multicolor changesduring the stretch and release processes, for example, betweenred, green, and blue. Both the high sensitivity and stability weremaintained after 1000 deformation cycles. These elastic pho-tonic-crystal fibers were woven into patterns and smart fabricsfor various display and sensing applications.

In nature, creatures such as the chameleon and cuttlefish arerenowned for their capability to rapidly change the color oftheir skin in response to the surrounding environment forcamouflage to escape or forage, communication, moodindication, and thermoregulation.[1, 2] The chromatic transi-tions typically arise from the translocation of pigments ora rearrangement of reflective units within a large number ofchromatophores.[1] The translation of natural structures andfunctionalities to artificial chromic materials and devices hasattracted increasing attention owing to a broad spectrum ofpromising applications, for example, as smart displays or insensing and actuation. Chromatic transitions in response tolight, temperature, chemical species, mechanical deformation,electricity, and magnetic fields have been extensively inves-tigated.[3–8] However, the conventional film shape of chro-matic materials and devices can hardly live up to therequirements for many applications, such as portable andwearable electronics. To this end, the use of fibers mayrepresent a promising strategy as fibers can be woven into

lightweight fabrics with another unique advantage, namelygood breathability.

Several chromic fibers have been realized based onelectrochromic materials.[9–11] For instance, carbon nano-tube/polydiacetylene composite fibers show a color changefrom blue to red that is due to a change in the conformation ofpolydiacetylene when an electric current is applied.[12] How-ever, the color change could only be reversed for tens ofcycles and only a limited number of colors could be displayed(mainly blue and red). Some efforts were also directedtowards incorporating different conjugated polymers into theelectrochromic layers.[13] However, to summarize, the above-mentioned thin electrochromic fibers are not stretchable andeasily break during use. Furthermore, electrochromism usu-ally needs a certain voltage, which causes various safetyproblems, particularly considering that these fibers are incontact with our body in many applications. Therefore, ourattention has shifted to mechanochromic materials, which canchange color under deformations such as bending andstretching. Mechanochromic devices exhibit several advan-tages over their competitors: They are safe and alsoconvenient for practical applications as such deformationsoften occur to wearable electric clothes during motion.Although photonic-crystal-based mechanochromic filmshave been widely explored,[14–18] mechanochromic fibershave hardly been realized. Recently, some attempts weremade to produce one-dimensional mechanochromic materialsby rolling up a film composed of two dielectric polymers or byextruding core–shell polymer particles.[19, 20] However, it isdifficult to produce a continuous fiber by scrolling a polymerfilm, and the requirement for hard–soft core–shell polymernanoparticles during extrusion limits the generalization inpreparing desired fiber materials and leads to low colorqualities.

Herein, a general and efficient strategy for the prepara-tion of continuous mechanochromic fibers with superiorproperties is described. The photonic-crystal fiber was madeby electrophoretically depositing polymer microspheres, suchas polystyrene (PS), onto a continuous sheet of aligned carbonnanotubes (CNTs) that had been wound on an elasticpoly(dimethylsiloxane) (PDMS) fiber, followed by furtherembedding in PDMS. The color of the photonic-crystal fibers,which arise from the assembly of polymer spheres, can betuned by the size of and the distance between the PSmicrospheres. In particular, the mechanochromic fiber, witha unique core–sheath structure and an elastic matrix, expe-riences rapid chromatic transitions during stretch and releaseprocesses with a high sensitivity and full reversibility, forexample, between the colors red, green, and blue. Both thehigh sensitivity and stability were maintained even after over

[*] Dr. X. Sun, J. Zhang, X. Lu, X. Fang, Prof. H. PengState Key Laboratory of Molecular Engineering of PolymersDepartment of Macromolecular Science, and Laboratory ofAdvanced Materials, Fudan UniversityShanghai 200438 (China)E-mail: sunxm@fudan.edu.cn

penghs@fudan.edu.cn

[**] This work was supported by MOST (2011CB932503), NSFC(21225417, 51403038), STCSM (12nm0503200), the China Post-doctoral Science Foundation (2047M560290), the Fok Ying TongEducation Foundation, the Program for Special Appointments ofProfessors at Shanghai Institutions of Higher Learning, and theProgram for Outstanding Young Scholars of the OrganizationDepartment of the CPC Central Committee.

Supporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/anie.201412475.

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1000 deformation cycles. The mechanochromic fibers werewoven into various patterns and fabrics for potential appli-cations in displays and sensing.

The preparation of mechanochromic fiber is illustrated inthe Supporting Information, Scheme S1. First, the elastic fiberwas prepared by curing the PDMS precursor in a tube-likemold with a typical diameter of 1.5 mm. Then, the alignedCNT sheets derived from spinnable CNT arrays werewrapped onto an elastic PDMS fiber through a rotation–translation strategy.[21] The thickness of the CNT sheathdepends on the width and helical angle of the CNT sheets. Inthe present study, the CNT sheaths had a thickness ofapproximately 330 nm, and the CNTs were highly aligned onthe elastic fiber (Figure S1). The black, conductive CNTsheath endowed the elastic fiber with a high conductivity sothat it can be used as the substrate and as an electrode.Afterwards, PS microspheres, with a typical diameter of200 nm, were deposited onto the elastic fiber by a fastelectrophoretic deposition (EPD) process.[22] Given that thePS microspheres are negatively charged, the conductiveelastic fiber was used as the anode with a stainless steelplate as the counter electrode. When an electric field wasapplied, the PS microspheres migrated towards the conduc-tive elastic fiber and rapidly assembled into a colloidal crystalstructure.[22] Later, PS microspheres were embedded in thePDMS precursors and cured to form the elastic photonic-crystal fiber. Finally, the mechanochromic photonic-crystalfiber was obtained after swelling and thermally grafting thevinyl-terminated silicon oil to the PDMS backbone. As thesyntheses of the PS microspheres, the aligned CNTs, and thePDMS substrate are technically mature processes, the wholeprocess is facile and fast and may be easily implemented in anindustrial setting.

In this fabrication process, the employed EPD methodrepresents one of the most effective processes for colloidalassembly to form photonic crystals, but it requires an electri-cally conductive substrate.[22] No fiber-shaped mechanochro-mic photonic crystals have been produced thus far owing toa lack of elastic and conductive fiber substrates. The surfacemorphology of the substrate also plays an important role inthe EPD process.[23] In our process, an elastic and conductivefiber substrate was obtained by winding aligned CNT sheetsonto the PDMS fiber, and the aligned structure can be wellmaintained with a stable resistance under stretching andreleasing (Figure S1). The aligned structure of the CNTs iscrucial as it is responsible for both the high conductivity andmechanical stability. When randomly dispersed CNTs wereused, the resulting fibers showed uneven surfaces with largeaggregates (Figure S2). Upon stretching, the random CNTswere ruptured with a distinct increase in resistance, and theoriginal resistance value could not be recovered after strainrelease (Figure S3). In another control experiment, conduc-tive graphene was coated onto the elastic fiber. Unfortu-nately, the resulting fiber became stiff; the graphene sheetscracked and peeled off from the PDMS substrate understretching (Figure S4).

The morphology of the 200 nm PS colloidal crystals on theconductive elastic fiber is shown in Figure 1a. The PSmicrospheres were uniformly deposited with a close-packed

structure on the surface and displayed a blue color (Figure 1a,inset). The aligned CNTs beneath the photonic-crystal layeralso affected the color of the fiber. As shown in Figure S5,when the thickness of the aligned CNTs was increased fromapproximately 40 and 100 to about 300 nm, the color of thefiber under otherwise identical conditions became more andmore vivid owing to absorption by the CNTs, which act likea black background.[24] Importantly, the reflection spectrawere similar because the reflection is mainly due to the PSmicrospheres. After infiltration with PDMS, the fiber hada uniform and smooth surface where the PS microsphereswere embedded completely (Figure 1b). The core–sheathstructure of the resulting fiber can be clearly seen in the cross-sectional images obtained with different microscopes. The PSmicrospheres and the CNT sheets, which formed a layer witha thickness of approximately 15 mm, were sandwichedbetween the inner PDMS fiber and an outer PDMS layer(Figure 1c–f; see also Figure S6). The high PDMS volumefraction (ca. 98%) leads to a highly sensitive elastic fiber,which will be discussed later. In addition, only a very thinlayer of the photonic crystal was required to obtain thedesired color.[22]

The diameter of the PS microspheres exerts an influenceon the initial colors and reflection peaks of the fiber. Bragg�s

Figure 1. Scanning electron microscopy (SEM) images of mechano-chromic fibers. a) The assembled 200 nm PS microspheres. Inset:Photograph of the fiber after deposition of the PS microspheres.b) Side view of the elastic mechanochromic fiber. c,d) Cross-sectionalview of the fiber in (b) at low (c) and high (d) magnification.e) Schematic illustration of the cross-sectional structure of the mecha-nochromic fiber. f) Cross-sectional optical micrograph of the mechano-chromic fiber. The light-colored section in the image indicates the200 nm PS microspheres that were deposited on the CNT sheets andembedded in PDMS.

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equation was thus used to elucidate the displayed color. Whenthe PS microspheres are stacked into a face-centered cubic(fcc) colloidal crystal, the wavelength of the reflection peakscan be approximately calculated by l = 2d neff =

(8/3)1/2D(0.74 np2 + 0.26nm

2�sin2q)1/2, where d, neff, D, np, nm,and q correspond to the (111) plane spacing, the effectiverefractive index, the diameter of the polymer spheres, therefractive index of the polymer spheres, the refractive indexof the matrix, and the angle between the incident beam andthe [111] direction of stacking, respectively.[25] Accordingly,when the incident light entered the fiber along its radialdirection, colloidal crystals made from PS microspheres (np =

1.59, nm = 1) with diameters of 200, 220, 240, 260, and 280 nmshould exhibit reflection peaks at wavelengths of 476, 524,572, 619, and 667 nm, respectively. In fact, the measuredspectra displayed reflection peaks at 448, 509, 533, 573, and624 nm, respectively (Figure S7). The blue shift with respectto the theoretical prediction was attributed to the reduction ofthe diameter of the PS microspheres during the dryingprocess, which was deduced to amount to approximately4.9% from the experimental results.[26] The defects and thecurved surface led to a slight broadening of the peaks in thereflection spectra compare to those of the ideal structure.After the fibers had been filled with PDMS elastomer andfurther grafted with silicon oil, the reflection peaks shifted tolonger wavelengths, that is, from 448 to 493 and 531 nm for the200 nm PS microspheres, and from 533 to 575 and 646 nm forthe 240 nm PS microspheres (Figure S8). These reflectionpeaks are in line with the color transitions from blue to greenand from green to red, which are caused by changes to thematrix and the increase in the center-to-center distancebetween the PS microspheres. As a result, the colors of theelastic photonic-crystal fibers depend on the size of depositedmicrospheres. A green and a red fiber, which were derivedfrom 200 and 240 nm PS microspheres, respectively, areshown in Figure 2 c and e.

Benefiting from its rubbery matrix, the photonic-crystalfiber has a decent elasticity, which enables the elongation ofthe fiber to produce color changes. As illustrated in Figure 2aand b, when stretched, the photonic-crystal fiber was axiallyelongated and shrunk radially; therefore, the lattice constantsof the assembled PS microspheres increase in the axialdirection and decrease in the radial direction. Given that thefiber color appeared selectively as a result of light diffractionin the radial direction, which complies with Bragg�s rule, thereflection peak was shifted to a shorter wavelength understretching. The color changes of the elastic photonic-crystalfibers from green to blue and from red to green undera mechanical strain of 30% are shown in Figure 2c–f. Afterrelease, the elastic photonic-crystal fiber regained its originalcolor, which indicates that the structural color transition isreversible.

The reversibility of the stretch/release deformations wasexamined for both bare PDMS and elastic photonic-crystalfibers (Figure S9). The stress of the photonic fiber was foundto be larger than that of a bare PDMS fiber under the samestrain, possibly owing to the presence of the stiff CNTs and PSmicrospheres. When stretched to a strain of 40 %, both fibermaterials could fully recover their original shapes after strain

release, and the above process could be repeated thousands oftimes, indicating the high elasticity and stability of thematerials. After stretching to 100 % or more and subsequentrelease, the bare PDMS fiber immediately fully recovered itsoriginal shape; a slight residual strain of approximately 5%was detected for the photonic-crystal fiber, which, however,still quickly recovered its original shape.

The mechanochromic behavior of the elastic photonic-crystal fiber was then characterized by reflection spectrosco-py. The evolution of the reflection spectra of the fiber duringthe stretching process is displayed in Figure 3a and c.Irrespective of whether the fibers were made from 200 nmor 240 nm PS microspheres, the reflection peaks were shiftedto shorter wavelengths, and the reflection intensities gradu-ally decreased. The dependence of the reflection peak on thestrain of the fiber made from 200 nm PS microspheres isillustrated in Figure 3b, and the peak was shifted from 531 to449 nm when the fiber was elongated by 30%. There was nodistinctive change in the reflection peak upon furtherstretching, implying that the PS microspheres were in contactwith each other in the radial direction and that no intervalspaces were available for a change in structure. Similar resultswere obtained for the fiber made from 240 nm PS micro-spheres. Its reflection peak shifted from 646 to 545 nm with anincrease in strain from 0 to 35%, but no changes wereobserved for a further increase in strain (Figure 3 c). Themechanochromic sensitivity, which is defined as Dl/De (thechange in the reflection peak relative to the percentageelongation), was measure to be approximately 2.8 nm/% onaverage for the photonic-crystal fiber and thus found to bemuch higher than that of the photonic-crystal films.[14, 18] Themechanochromic behavior of the elastic photonic-crystalfiber had a remarkable reversibility. As demonstrated inFigure 3d, after the mechanical strain had been removed, thereflection peak of the photonic-crystal fiber returned to itsoriginal position. The transition could be repeated for over1000 cycles with strains between 0 and 15 %, indicating thatthe structure of the elastic photonic-crystal fiber is highlystable.

Upon stretching with a strain e, the lattice constants of theassembled PS microspheres decrease to 1�ne in the radialdirection where n is the Poisson ratio of the fiber.[27] Theposition of the reflection peak can then be linearly expressed

Figure 2. Mechanochromic fibers. a, b) Schematic illustration of thestructure changes of the fiber under stretching. c, d) Photographs ofthe mechanochromic fiber made from 200 nm PS microspheres before(c) and after (d) stretching. e, f) Photographs of the mechanochromicfiber made from 240 nm PS microspheres before (c) and after (d)stretching.

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as le = 2d111 neff = l0(1�ne), where l0 and le are the reflectionpeaks of the fiber prior to and under stretching. This equationexplains the blue shift of the color under stretching. By fittingthe experimental data to this equation, a n value of approx-imately 0.455 was calculated for a strain of less than 30 %,which is much higher than the value reported for a mechano-chromic film and close to that of the bare PDMS elastomer(0.5), suggesting that the photonic-crystal fiber was homoge-neously stretched like an elastic material.[18, 27] This conclusionwas corroborated by the increase in the axial distancebetween the PS spheres when the material was stretched by30% (Figure 3e, f). At the same time, the lattice distance inthe radial direction of the fiber must decrease until the PSmicrospheres are in contact with each other, which explainsthe blue shift of the reflection peaks. At higher strains, forexample, at 50 % strain, the arrangement of the microsphereschanged from hexagons to squares (Figure 3g), similar to thepreviously reported film.[27] The decay of the reflectionintensity is primarily attributed to the decrease in the opticaldielectric contrast between the PS spheres and PDMS understretching and possibly also to the order loss in the radialdirection of the PS colloidal crystal.[28, 29] After release, the

elastic PDMS substrate recovered itsoriginal arrangement benefitting fromthe core–sheath structure of the fiberwith a thin photonic-crystal sheath(thickness ca. 15 mm) and a thickPDMS fiber core (diameter 1.5 mm).The relation between l and e can thenbe expressed as le = l0(1�0.455e) forstrains of� 30%; the wavelength of thereflection peak can thus be tuned byvarying the strain of the fiber.

Owing to its one-dimensional con-figuration and mechanochromic prop-erties, the elastic photonic-crystal fibermay find applications in displays andsensing devices. For example, the fiberscan be woven into chromatic fabrics forfashionable and individual wearableitems, avoiding the use of organic dyesor pigments. In Figure 4a–c, severalcolorful patterns that were preparedwith different elastic photonic-crystalfibers are shown. Owing to their intrin-sic structural color, the patterns arefade-resistant and durable. Moreover,the mechanochromic performancemakes the fiber sensitive and respon-sive to mechanical strain, which can beused to map the stress distribution or tomonitor the movement of a body, forexample. A fabric cross-woven fromgreen and red elastic photonic-crystalfibers is shown in Figure 4d–g. Fourcolor combinations can be realized byapplication of various strain combina-tions. For instance, when stretched inthe vertical direction, the fabric became

red and blue as the green fibers turned blue, whereas it onlydisplayed a green color on stretching in the horizontaldirection because the red fibers turned green. When bilat-erally stretched at the same time, the fabric displayed thecolors green and blue. As a pH test paper can indicate theacidity and alkalinity in color, the mechanochromic photonic-crystal fiber can visualize the applied strain as a load sensor.As shown in Figure S10, fibers loaded with different weightsexhibited different colors. Once a correlation between theweight and the position of the reflection peak of the fiber hasbeen established, it will be a viable approach to visualize theload.

The observed color varied in the radial direction, with themiddle section appearing to be brighter than the side as theywere not in the same plane owing to the curved fiber surface.This iridescence phenomenon has been intensively studied forhighly ordered photonic crystals. To suppress the iridescenceeffects, two PS microspheres with different diameters weresimultaneously deposited onto an aligned CNT sheet to forma disordered structure (Figure S11).[30, 31] More efforts areunderway to achieve bright and saturated colors in mimickingnature.

Figure 3. Mechanochromic performance of the elastic photonic-crystal fiber. a) Reflection spectraof the fiber made from 200 nm PS microspheres under different strains. b) Variation of the peakposition with strain in (a). c) Reflection spectra of the fiber made from 240 nm PS microspheresunder different strains. d) Evolution of the peak position over 1000 cycles of stretching (15%strain) and releasing. The elastic photonic-crystal fiber was prepared with 200 nm PS micro-spheres. e–g) SEM images of a colloidal crystal layer on the surface before (e) and afterstretching to 30% (f) and 50% (g). The fiber was stretched along the horizontal direction.

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In conclusion, a new family of multicolored mechano-chromic photonic-crystal fibers was synthesized by a fast andfacile process. These fibers exhibit brilliant color changes andobvious reflection peak shifts in the visible-light range undermechanical strains from 0 to 30 % and maintained very highsensitivity, reversibility, and stability for thousands of cyclesowing to the unique core–sheath structure. These elasticphotonic-crystal fibers can be woven into smart fabrics withpromising applications as fashionable displays and for strainmapping and sensing. A general and effective route for theindustrial production of novel photonic-crystal fibers has alsobeen presented.

Received: January 2, 2015Published online: February 27, 2015

.Keywords: carbon nanotubes · fibers · materials science ·mechanochromic properties · photonic crystals

[1] A. V. Singh, A. Rahman, N. V. G. Sudhir Kumar, A. S. Aditi, M.Galluzzi, S. Bovio, S. Barozzi, E. Montani, D. Parazzoli, Mater.Des. 2012, 36, 829.

[2] D. Stuart-Fox, M. J. Whiting, A. Moussalli, Biol. J. Linn. Soc.2006, 88, 437.

[3] J. Ge, Y. Yin, Angew. Chem. Int. Ed. 2011, 50, 1492; Angew.Chem. 2011, 123, 1530.

[4] J. Cui, W. Zhu, N. Gao, J. Li, H. Yang, Y. Jiang, P. Seidel, B. J.Ravoo, G. Li, Angew. Chem. Int. Ed. 2014, 53, 3844; Angew.Chem. 2014, 126, 3923.

[5] K. Hwang, D. Kwak, C. Kang, D. Kim, Y. Ahn, Y. Kang, Angew.Chem. Int. Ed. 2011, 50, 6311; Angew. Chem. 2011, 123, 6435.

[6] C. G. Sch�fer, M. Gallei, J. T. Zahn, J. Engelhardt, G. P.Hellmann, M. Rehahn, Chem. Mater. 2013, 25, 2309.

[7] X. Sun, T. Chen, S. Huang, L. Li, H. Peng, Chem. Soc. Rev. 2010,39, 4244.

[8] Y. Zhao, Z. Xie, H. Gu, C. Zhu, Z. Gu, Chem. Soc. Rev. 2012, 41,3297.

[9] X. Sun, Z. Zhang, X. Lu, G. Guan, H. Li, H. Peng, Angew. Chem.Int. Ed. 2013, 52, 7776; Angew. Chem. 2013, 125, 7930.

[10] P. M. Beaujuge, J. R. Reynolds, Chem. Rev. 2010, 110, 268.[11] W. M. Kline, R. G. Lorenzini, G. A. Sotzing, Color. Technol.

2014, 130, 73.[12] H. Peng, X. Sun, F. Cai, X. Chen, Y. Zhu, G. Liao, D. Chen, Q. Li,

Y. Lu, Y. Zhu, Q. Jia, Nat. Nanotechnol. 2009, 4, 738.[13] K. Li, Q. Zhang, H. Wang, Y. Li, ACS Appl. Mater. Interfaces

2014, 6, 13043.[14] E. P. Chan, J. J. Walish, A. M. Urbas, E. L. Thomas, Adv. Mater.

2013, 25, 3934.[15] D. Yang, S. Ye, J. Ge, Adv. Funct. Mater. 2014, 24, 3197.[16] H. Feng, J. Lu, J. Li, F. Tsow, E. Forzani, N. Tao, Adv. Mater.

2013, 25, 1729.[17] F. Castles, S. M. Morris, J. M. C. Hung, M. M. Qasim, A. D.

Wright, S. Nosheen, S. S. Choi, B. I. Outram, S. J. Elston, C.Burgess, L. Hill, T. D. Wilkinson, H. J. Coles, Nat. Mater. 2014,13, 817.

[18] H. Fudouzi, T. Sawada, Langmuir 2006, 22, 1365.[19] M. Kolle, A. Lethbridge, M. Kreysing, J. J. Baumberg, J.

Aizenberg, P. Vukusic, Adv. Mater. 2013, 25, 2239.[20] C. E. Finlayson, C. Goddard, E. Papachristodoulou, D. R.

Snoswell, A. Kontogeorgos, P. Spahn, G. P. Hellmann, O. Hess,J. J. Baumberg, Opt. Express 2011, 19, 3144.

[21] Z. Yang, J. Deng, X. Sun, H. Li, H. Peng, Adv. Mater. 2014, 26,2643.

[22] N. Zhou, A. Zhang, L. Shi, K.-Q. Zhang, ACS Macro Lett. 2013,2, 116.

[23] Z. Liu, Q. Zhang, H. Wang, Y. Li, Nanoscale 2013, 5, 6917.[24] Z. Shen, L. Shi, B. You, L. Wu, D. Zhao, J. Mater. Chem. 2012, 22,

8069.[25] Z. Liu, Q. Zhang, H. Wang, Y. Li, Chem. Commun. 2011, 47,

12801.[26] A. L. Rogach, N. A. Kotov, D. S. Koktysh, J. W. Ostrander, G. A.

Ragoisha, Chem. Mater. 2000, 12, 2721.[27] B. Viel, T. Ruhl, G. P. Hellmann, Chem. Mater. 2007, 19, 5673.[28] K. Matsubara, M. Watanabe, Y. Takeoka, Angew. Chem. Int. Ed.

2007, 46, 1688; Angew. Chem. 2007, 119, 1718.[29] J. F. Bertone, P. Jiang, K. S. Hwang, D. M. Mittleman, V. L.

Colvin, Phys. Rev. Lett. 1999, 83, 300.[30] J.-G. Park, S.-H. Kim, S. Magkiriadou, T. M. Choi, Y.-S. Kim,

V. N. Manoharan, Angew. Chem. Int. Ed. 2014, 53, 2899; Angew.Chem. 2014, 126, 2943.

[31] L. Shi, Y. Zhang, B. Dong, T. Zhan, X. Liu, J. Zi, Adv. Mater.2013, 25, 5314.

Figure 4. Chromatic patterns and fabric made from elastic photonic-crystal fibers. a–c) Colorful patterns woven from different photonic-crystal fibers. d–g) Schematic illustration and photographs of themechanochromic fabrics under different manipulations in their initialstate (d), under vertical stretching (e), under horizontal stretching (f),and under bilateral stretching (g).

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